When pipe welding in the field, the joint between the ends of pipe sections is essentially the same as a joint between two heavy plates, except the pipe joint to be welded includes an open root where the ends of the pipe are spaced slightly. This open root is a gap normally created by bringing the two pipe sections into abutting relationship, followed by a withdrawal of a selected amount to define the minimum open root in the joint. It is essential that this open root be welded together with a quality weld throughout the total thickness of the bottom area of the pipe joint; however, when laying the first bead in the open root, it is also necessary that the molten weld metal does not protrude inwardly of the pipe section to any substantial distance. The pipe must be clear so that a pig and other cylindrical devices can move through the pipe section without encountering inwardly protruding weld metal created during the open root first welding. As another consideration, the heat of the open root weld cannot be too high causing metal shrinkage and, thus, draw back into the gap forming the open root. To accomplish a quality pipe open root weld, without substantial inward protrusion of molten metal or metal draw back, a short circuit arc welding method of the type made possible by use of an STT electric arc welder has been adopted. This pipe welding process controls the initial welding pass of the pipe welding procedure to fill the open root. Although this type of welding process is extremely advantageous, a substantial amount of development work has been required to select the welding wire to be used during the short circuit welding process. It has been found that a cored electrode has substantial advantages when used with an STT electric arc welder in welding the joint between pipe sections; however, the open root pass weld bead presents unique welding challenges. It has been found that the root pass weld bead is best accomplished by using a solid wire with the characteristics of the ANSI-AWS A 5. 1895 solid welding wire. This type of welding wire is used with a shielded gas and has the following specification.
TABLE I ______________________________________ Percentage ______________________________________ Carbon .06-.15 Manganese .90-1.40 Silicon .45-.75 Phosphorous 0-.025 Sulfur 0-.035 Copper 0-.50 Ni/Cr/Mo/V 0-.50 ______________________________________
This standard gas shielded welding wire has been selected as a welding wire which provides a good appearance and allows the advantages of the STT electric arc welder during the open root welding pass. Although the weld bead appearance is usually acceptable with standard solid wire, a substantial improvement in bead appearance is obtained on the top and bottom of the bead by using the present invention.